The long-term objective of this proposal is to develop and immunization protocol which significantly protects laboratory hosts against infection by Schistosoma mansoni. To achieve this objective, the following specific aims have been established: (I) Protein antigens of the protection-inducing, 4 week stage of the parasite, which react uniquely with antibodies in a protective immune rat serum (Fischer strain), will be isolated by sequential lectin-and immuno-affinity chromatography. Further purification of antigens by ion-exchange or molecular sieving chromatography will be conducted. (II) Immunization protocols using purified protein antigen fractions will be developed to ascertain the capacity of these antigens to induce resistance to an infection. An analysis of the types of antibodies produced in response to injection of purified antigens will include a search for relationships between protective activity and the class distribution of the induced antibodies. From the results of this analysis, an opportunity may arise to improve upon the degree of induced resistance which results during natural infection. (III) Recombinant DNA methodology will be applied in an effort to generate continuous cell cultures capable of producing the relevant protein antigens in quantities required for immunization. Through these above efforts, it is hoped that sufficient information will be acquired for applying this methodology as one of the approaches necessary to control the highly prevalent disease, human schistosomiasis.